It may be desirable to induce a strain in the channel region of a semiconductor device in order to improve performance. Strained silicon in the channel may be produced in a number of manners. For example, silicides in source and/or drain regions can induce strain in channels of metal-oxide-semiconductor MOS devices. In a MOS field effect transistor (MOSFET) a silicide in the source/drain (SD) is typically a result of the reaction of a metal layer with SD/channel materials of the MOSFET. The resulting strains induced on the channel by silicides originate from the difference in coefficients of thermal expansion between the silicide and the substrate/channel material. More specifically, as the device cools from the final silicide phase, the difference in the coefficients of thermal expansion of the silicide and channel material result in the silicide contracting more than the channel material. A tensile stress is, therefore, induced in the channel. However, the magnitude of the stress achievable by this mechanism may be limited. Alternatively, a metal film can be reacted with a semiconductor to the form a compound (e.g. a silicide) that occupies less volume than the combined volumes of the unreacted metal and semiconductor layers. Although some tensile strain may be developed using this method, a significant drawback is the formation of voids.
Consequently, an improved mechanism for providing tensile strain in the channel of a MOS device is desired.